CMC Medical CMC-Medical VELLORE Solved Paper-2008

  • question_answer
    The excess of pressure inside the first soap bubble is three times that inside the second bubble. The ratio of volume of the first to that of the second bubble is

    A)  1 : 3                                      

    B)  1 : 9

    C)  1 : 27                                    

    D)  9 : 1

    E)  27 : 1

    Correct Answer: C

    Solution :

                    Excess of pressure inside a soap bubble \[p=\frac{4T}{R}\] or            \[\frac{{{p}_{1}}}{{{p}_{2}}}=\frac{{{R}_{2}}}{{{R}_{1}}}\] Given \[{{p}_{1}}=3{{p}_{2}}\] \[\therefore \]  \[\frac{3{{p}_{2}}}{{{p}_{2}}}=\frac{{{R}_{2}}}{{{R}_{1}}}\] or            \[\frac{{{R}_{1}}}{{{R}_{2}}}=\frac{1}{3}\] Therefore, ratio of volumes of bubbles \[\frac{{{V}_{1}}}{{{V}_{2}}}=\frac{\frac{4}{3}\pi {{R}_{1}}^{3}}{\frac{4}{3}\pi {{R}_{2}}^{3}}\] \[=\frac{{{R}_{1}}^{3}}{{{R}_{2}}^{3}}={{\left( \frac{1}{3} \right)}^{3}}=\frac{1}{27}\] \[\therefore \]  \[{{V}_{1}}:{{V}_{2}}=1:27\]


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